Catalytic cracking of hydrocarbons



C. L. THOMASI CATALYTIC CRACKING OF HYDROCARBONS July 6, 1948.

2 Sheets-Sheet 1 Filed Feb. 18, 1944 a 5 NL l gf@ WM E, D@ .mwNm

Juy 6, i948. c. L. THOMAS' Y CATALYTIC CRACKING OF HYDROCARBONS 2 'Sheets-Sheet 2 Filed Feb. 18, 1944 ,NN WK lunv Patented July 6, 1943 y 2,444,545 CATALYTICCRACKING or rivnraoonnnoNs Charles L. Thomas, Riverside, Ill., assigner to Universal Oil Products Company, Chicago, Ill., a corporation of Delaware f Application February 18, 1944, Serial N0. 522,855

This application is -a continuation-impart of imy co-pending application Serial No. 296,067, filed September 22, 1939, now abandoned.

This invention relates to a process for converting hydrocarbon oil to motor fuel and more particularly to the production of a c-atalytically cracked gasoline vsuitable for use .as an aviation base fue It is desirable in aviation basefuels that they have a low content of olefinic hydrocarbons which tend to develop gum during extended periods of storage.

The present invention concerns a method of producing high yields ofrelatively saturated aviation base stock by means of catalytic conversion of hydrocarbon oils. v v

Broadly, the invention relates to a process for converting hydrocarbon oil into substantial yields of relatively high antiknock motor fuel having la high degree of susceptibility to lead tetraethyl which comprises contacting said hydrocarbon oil with a cracking catalyst ina primary cracking step at a temperature of 50G-900 F. and at cracking conditions to effect moderate conversion and produce a relatively saturated gasoline, separating said gasoline, contacting the insufficiently converted oil from the primary step with a cracking catalyst in a secondary cracking step at a temperature of approximately. 9001200 Fand at cracking conditions to effect a high degree of conversion and produce aA relatively olefin-free giasoline, and separating said last mentioned gaso ine.

In a more specific embodiment the present invention comprises a process for converting hydrocarbon oilv into substantial yields of relatively high antiknock fuel in Whichsaid hydrocarbon oil is contacted with a cracking catalyst in a primary cracking step at a temperature o-f 50G-.900 F. and at cracking conditions to effect moderate conversion and produce a relatively saturated gasoline, separating saidgasoline, contacting the insuiiiciently converted oil from the primary step with a cracking catalyst in a secondary cracking step at a temperature of approximately S200-'1200o F. and at cracking conditions adequateto effect a high degree of conversion and produce a relatively saturated highly aromatic gasoline and an intermediate highly aromatic fraction, separating said last mentioned gasoline and blending it with said first mentioned gasoline, and returning said highly aromatic intermediate fraction to the primary cracking step to undergo conversion with said hydrocarbon oil.

In the cracking of hydrocarbon oils, `conversior'i has beendened by several different means. For

2 example, conversion may be defined as the quantity of a particular yboiling range gasoline fraction produced as compared to the original charge. It also may be defined Aasthe percentage by weight of the charge which is converted to gasoline plus gas 'plus' coke. I prefer the latter definition lfor conversion and hereinafter in this specification and claims, unless otherwise noted, conversionis intended to have this preferred meaning. y

It has been found when treating a virgin cracking stock thaty low temperatures and moderate conversions result in the most economical yield of relatively saturated high antiknock motor fuels suitable for aviation base stock. The degree of conversion which is attained in catalytic cracking processes is dependent upon several factors including the particular catalyst employed, the charging rate of the material to be cracked, the ratioof regenerated catalyst to the quantity of oil treated, and the temperature of operation. Inl general, conversion increases With increases in temperature, and increases in the ratio of catalyst to oil and decreases with increases in the `charging rate of the material to be cracked. Of the several operating variables which must be considered in catalytic cracking those Which have the greatest effect on product quality are conversion and the character of the hydrocarbon oil being treated. For example, with increases inv conversion the saturation of the product increases as well as the -aromatic content. As the character of the charging stock is changed from paraffinic to na'phthenic the saturation of the product increasesr and the aromatic content of the product increases. y

In relating gasoline yield to conversion, it has been found that the gasoline yield increases with' conversion to a maximum and then declines as the conversion increases further. The point of' maximum gasoline yield decreases as the temperature increases. In the process herein disclosed the virgin cracking stock is treated ata cracking temperature under about 900 F. and at a moderate conversion corresponding to a point in the conversion against gasoline yield curve which'l In the second stage of my process I intend treating the more refractory insufficiently converted hydrocarbon oil from the first stage to produce a relatively saturated product containing a high proportion of aromatic hydrocarbons. In this step of the process I intend operating to obtain a conversion which corresponds to a point on the conversion against gasoline yield curve which is on the high conversion side of the maximum gasoline yield point which will, with refractory stocks, be not less than a conversion of about 60% by weight of the charge, It has been found that when operating at the high conversions contemplated for use in this invention, a saturated gasoline product containing a high percentage of aromatic hydrocarbons is produced. However, in order to obtain the high conversion and the aromatic gasoline necessary to satisfactorily accomplish my invention, it is necessary when using the refractory stock from the rst vstep to operate at temperatures above about 900 F.

In the more specific embodiment of the invention wherein the intermediate aromatic fraction (300-450 F. boiling range) produced in the high temperature step is to be converted to gasoline boi-ling range aromatics, it has been found that more selective dealkylation of the poly alkylated aromatics present in this material may be kobtained `when the temperature conditions of conversion are below about 900 F. It is, therefore, one of the features of this invention to return this material to the low temperature step of the process in order to more selectively dealklate the aromatics to produce alkylated aromatics which are more suitable for use in aviation gasoline.

Catalytic materials useful in the primary and secondary cracking steps of this process include any suitable cracking catalyst but are preferably of the synthetic precipitated silica-alumina, silica-zirconia, and silica-alumina-zirconia type. The catalyst may be employed in the form of pills, granules, or powder depending upon the particular apparatus in which is to be used. For example, in xed or moving bed processes the -pilled or granular forms are in general more desirable, while in the so-called fiuidized bed processnely-dvided catalyst in the form of powder or small granules or formed particles will give excellent results.

Although the present process ,is usually operated with a similar catalytic agent in both the primary and secondary cracking steps it is well Within vthe scope of the invention to use a different `catalytic mass in each step.

During the cracking reaction there is an accumulation of carbonaceous or `hydrocarbonaceous material on the catalytic surface which reduces their activity. These materials are ordinarily removed by burning in an oxygen containing gas toreactivate the catalyst.

When employing a fixed bed process the catalyticmass is alternately contacted with reactant materials and with the oxygen containing gas with the necessary purging steps intermediate the other two periods of the process. When employing moving bed or uidized bed processes, the catalyst is ordinarily transferred between the reaction zone wherein itis contacted with the reactant material and the regenerating zone wherein. it is contacted with oxygen containingk gas. The` transportation of the catalyst between the two zones may be accomplished by various means including mechanical conveyors and elevators. ln` some cases the reactant materials and regenerating gas are used as transportation means for the catalyst.

In order to make the invention more apparent and thoroughly understood reference is made to the accompanying diagrammatic drawing.

Figure l of the drawing illustrates one form of apparatus suitable for conducting the pro-cess of the invention. In this particular form separate fractionating columns are provided for the two cracking steps.

Figure 2 illustrates an alternative form of apparatus suitable for conducting the process of the invention in which a single fractionating column is employed for-both cracking steps.

Referring now to Figure l, the charging stock is supplied through line I and valve 2 by means of pump 3 to heating coil 4 located in heater 5. In the heating coil the charging material is heated to a temperature of from 50G-900 F. and is then directed through line 6 and valve I into reactor 8. 'Ihe apparatus illustrated is of the fixed bed. type and only a single reactor is shown. However, in .practice in order to obtain continuity of operation at least two reactors Wouldibe employed, in order that while one is being regenerated the other may be processing the reactant material.

The reactionv products from the reactor aredirected through line 9 and valve I0 into fractionatorrII wherein an overhead product having the desired end boiling point is separated from the insufficiently converted material. The overhead product is passed through line I2 and valve I3 into condenser I4 wherein the product is cooled and the resultant distillate is directed by means of line I5 and valve I 6 into receiver I1. In receiver I'I the uncondensed gases are separated from the condensate and are removed from the system throughline I 8 and valve I9. The condensate is vremoved from the system through line 20 and valve 2|.

The insufficiently converted material from the first step is removed from fractionator II through line 22 and valve 23 andl directed by means of pump 24 into heating coil 25 disposed within heater 26. The oil passing through coil 25 is heated to a temperature of from aboutv900 F. to about 1200 F. and then directed by means of line '21 and valve 28 into reactor 23. Although only one reactor is shown in the drawing it is to be understood that in practice a plurality of such reactors .would be employed. From reactor 29, the reaction products are directed by means of line 30 and valve 3| into fractionator v32. An overhead product having the desired end boiling point islremoved by means of line 33 and valve 34 and directed into condenser 35. `The cooled material from condenser 35 is then directed through line 36 and valve 31 into receiver 38. In receiver 38 the uncondensed gases are separated from the condensate and the former is removed irom the system through linev 39 and valve 40. The condensate is removed from the system through line 4i and valve 42 and commingled with the condensate produced in the iirst stage of the process to be directed to suitable equipment for stabilization and the like.

The insufliciently converted material is re intermediate fraction boiling from about 300 tol 450 F. is removed from fractionator 32 by means of line 41 and valve 43 to be commingled with the charging stock passing through line I.

Referring now to Figure 2, charging stock for the process is introduced through line 50 controlled by'valve 5l and discharged from pump 52 into heating coil 53 disposed within heater 54. The oil passing through coil 53 is heated to a temperature of from about 50G-900 F. and then passed -through line 55 and valve 56 into reactor 51. The reaction products from reactor 51 are passed through line 58 and valve 59 into fractionator 60. The insulciently converted material removed from the bottom of fractionator 60 is passed through line 6|, valve 62, and pump E3 into heating coil 64 disposed within heater 65. In heating coil 64 the oil is heated to a temperature of from about 9001200 F. and then passedthroughl line 66 and valve 61 into reactor 68. The resultant conversion products are removed from reactor 68 by means of line 69 and valve 10, commingled with the material passing through line 58 and thence directed into fractionator 60. The overhead product from fractionator 60 containing the desired end point gasoline is withdrawn through line 1| and valve 12 and passed into condenser 13. The cooled material from condenser 13 is then directed by line 14 into receiver 15. In receiver 15 the uncondensed gases are separated and removed from the process through line 16 and valve 11 and the resultant liquid condensate is removed from the system through line 18 and valve 19. An intermediate naphtha fraction high in aromatics is withdrawn from fractionator 60 by means of line 19' and valve 80 and commingled with the charging stock in line 50 or when desired this material may be withdrawn from the system through line 8| and valve 82.

In order to further illustrate the utility of the invention the following example is included. It is, however, not to be construed as a limitation of the invention.

A Mid-Continent gas oil having a gravity of 37.1 A. P. I. is passed into the rst stage reactor which is maintained at about 825 F. and slightly superatmospheric pressure. The charging material is passed through the catalyst bed at a weight hourly space velocity of 2 and the process period length. is regulated to give a conversion of 40%. The resultant gasoline and gas are separated from the insuihciently converted material and the latter is then passed through a second stage reactor maintained at 950 F. and slightly superatmospheric pressure. The materials undergoing conversion are passed through the catalyst mass at a weight hourly space velocity of 1.8 and the process period length' is regulated to give a conversion of 65%. The gasoline and gas are separated from the insufliciently converted material and the latter recycled through the second stage of the process. The gasoline and gas produced in each of the stages are mixed and the following is a tabulation of the yields obtained in the process:

Yield wt. percent of the charge 300 F. E. P. depent, gaso 44.5 Carbon 9.3 C3, C4, C5 OleflllS 16.5 Isobutane 11.7 Isopentane 8.2 Normal C5- and dry gas 9.8

Total 100.0

The above gasoline whichcontains 45% aromatics has a bromine number of 1'1 and has a 1C rating with 4 cc. of tetraethyllead of 96. The isopentane produced may be used to increase the vapor pressure of the gasoline and at'the same time increase its antiknock rating. The higher olefins and isobutane may be converted into alkylates and polymers which have a high' aviation gasoline blending value.

The l-C method is described in A. S. T. M.

I claim as my invention:

1. A process for the production of substantially saturated gasoline which comprises introducing a hydrocarbon oil into a primary cracking zone and therein contacting said oil with a cracking catalyst at a cracking and dealkylating temperature below about 900 F., correlating the charge rate of said hydrocarbon oil to said primary cracking zone and the ratio of catalyst to oil in said zone with said cracking temperature to eilect a conversion of said hydrocarbon oil of not more than 60% and to produce a substantially saturated gasoline, separating from the resultant products said substantially saturated gasoline and a higher boiling insufli-ciently converted hydrocarbon oil, introducing the latter into a secondary cracking zone and therein contacting said insufficiently converted hydrocarbon oil with a cracking catalyst at a cracking temperature above about 900 F., correlating the charge rate of hydrocarbon oil to said secondary cracking zone and the ratio of catalyst to oil therein with said last named cracking temperature to eiect a conversion of said insufficiently converted hydrocarbon oil of at least 60% and to produce a substantially saturated gasoline, separating from the reaction products of said secondary cracking zone said last named gasoline and a polyalkylaromatic fraction boiling within the range of from about 300 F. to about 450 F., and recycling said polyalkylaromatic fraction to said primary cracking Zone to selectively dealkylate the same at said dealkylating temperature.

2. The process of claim 1 wherein the catalyst employed in each of said cracking zones consists of a composite of silica and alumina.

3. The process of claim l wherein the catalyst employed in each of said cracking zones consists of a composite of silica and zirconia.

4. The process of claim 1 wherein the catalyst employed in each of said cracking zones consists of a composite of silica, alumina, and zirconia.

5. The process of claim 1 further characterized in that the conversion in said primary cracking zone is from about 25% to about 60%.

6. A process for the production of substantially saturated gasoline which comprises introducing a hydrocarbon oil into a primary cracking zone and therein contacting said oil with a cracking catalyst at a cracking and dealkylating temperature below about 900 F., correlating the charge rate of said hydrocarbon oil to said primary cracking zone and the ratio of catalyst to oil in said zone with said cracking temperature to effect a conversion of said hydrocarbon oil of not more than 60% and to produce a substantially saturated gasoline, introducing the resultant products into a fractionating zone and withdrawing therefrom insufciently converted hydrocarbon oil, introducing the latter into a secondary cracking zone and therein contacting said insuciently converted hydrocarbon oil with a cracking catalyst at a cracking temperature above about 900 F., correlating the charge rate of hydrocarbon oil to 7 said'secondary cracking zone and the ratio of cat-v alyst to oil therein with said last named cracking temperature to effect a conversion of said insuici'ently converted hydrocarbon oil of at least 60% and toprodnce a substantially saturated gasoline, introducing the reaction products from said secondary cracking zone into said fractionating zone, separating in said fractionating zone a substantially saturated gasoline fraction and a polyalkylaromatic fraction boiling within the range of from about 300 F. to about 450 F., and recycling said polyalkylaromatic fraction to said primary cracking zone to selectively dealkylate the same at said dealkylating temperature.

CHARLES L. THOMAS.

REFERENCES CITED UNITED STATES PATENTS Number Name Date 2,051,612 Loebel Aug. 18, 1936 2,203,850 Tropsch June 11, 1940 2,214,455 Egloff et al. Sept. 10, 1940 2,272,297 Gerh'old Feb. 10, 1942 2,297,773 Kanhofer Oct. 6, 1942 2,300,031 Benedict Oct. 27, 1942 2,342,080 Kalichevsky Feb. 15, 1944 2,377,613 Conn June 5, 1945 2,390,556 Ruthruff Dec. 11, 1945 2,397,329 Ruthrui Mar. 26, 1946 OTHER REFERENCES Murphree et al., National Petroleum News, Dec. 1, 1943, pages Rf-577 and R-578. This is a portion of a paper presented before the Division of Rening, A. P. I., Chicago, on Nov. 11, 1943. (Copy in Scientific Library.) 

